The present invention relates generally to a system and method for extending the ITU Q.922 LAPF (link access procedures for Frame Mode bearer services) virtual circuit disconnect logic. More specifically, a system and method for extending and modifying the ITU Q.922 LAPF disconnect logic to remedy or alleviate instances of unsynchronized virtual circuit establishment are disclosed.
Frame Relay is a packet switching protocol for connecting devices on a wide area network (WAN). Frame Relay operation is in part specified by ITU Recommendation Q.922 (Geneva, 1992) entitled “ISDN Data Link Layer Specification For Frame Mode Bearer Services” published by the ITU. Recommendation Q.922 relates to the Digital Subscriber Signaling System No. 1 (DSS 1) data link layer and specifies the frame structure, elements of procedure, format of fields and procedures of the data link layer to support frame mode bearer services in the user plane (U-plane) as defined in ITU Recommendation I.233 (frame mode bearer services).
Recommendation Q.922 contains a deficiency in that it is possible to have instances of unsynchronized SVC establishment due to one device going through system reboot and shutting down all active SVCs while a peer device believes that these SVCs are still active. To mitigate this deficiency, it has been suggested that, at the first attempt of bringing up the L2 (layer 2) link during system re-initialization, a DISC (disconnect) message be transmitted prior to the specified transmission of a SABME (Set Asynchronous Balanced Mode Extended) message. The SABME message is in essence a message for requesting establishment of the link. The SABME and DISC messages are defined by ITU Recommendation Q.921. According to this proposed solution, the DISC message is transmitted in all situations in which link layer services (LAPF) are restarted.
However, the proposed solution does not satisfactorily or fully resolve the unsynchronized SVC establishment issue. Therefore, what is needed is a system and method for extending and modifying the ITU Q.922 LAPF disconnect logic to better remedy or alleviate instances of unsynchronized SVC establishment.